The present invention relates to a method of controlling transport amounts of recording mediums, in which the recording mediums are being transported in a state in which the recording mediums are nipped between a pair of transport rollers and a pair of ejecting rollers, the pair of transport rollers transporting the recording mediums to the side of a recording head from a feed portion in which the recording mediums are laminated, the pair of ejecting rollers ejecting the recording mediums on which recording is performed by a recording head, a transport device, a recording apparatus having the transport device, and a liquid ejecting apparatus having the transport device.
Examples of a liquid ejecting apparatus include recording apparatus, such as an inkjet recording apparatus that ejects ink from a recording head serving as a liquid ejecting head to recording mediums, such as recoded paper, and performs recording on the recording mediums, a copy machine, a facsimile, and the like, and apparatuses that eject liquid corresponding to a specific use other than the ink onto ejected members corresponding to the recording mediums from a liquid ejecting head corresponding to the above-mentioned recording head and adhere the liquid to the ejected members. Further, examples of the liquid ejecting head include, in addition to the above-mentioned recording head, a colored member ejecting head that is used for manufacturing a color filter of a liquid crystal display, an electrode member (conductive paste) ejecting head that is used for forming electrodes of an organic EL display or a field emission display (FED), a living-body organic matter ejecting head that is used for manufacturing a biochip, a sample ejecting head that ejects a sample as a precise pipette, and the like.
As an example of the inkjet recording apparatus or the liquid ejecting apparatus, there is provided an inkjet printer. The inkjet printer includes a feed portion that feeds laminated recording mediums to a downstream-side transport path, a transport portion that transports the fed recording mediums to a recording portion, the recording portion that performs recording on the recording mediums, and an ejecting portion that ejects the recording mediums on which recording is performed. Among them, the transport portion has a pair of transport rollers that transport the recording mediums from the feed portion to the recording portion at the downstream side of the recording portion. Further, the recording portion has a recording head that ejects ink onto the recording mediums. Furthermore, the ejecting portion has a pair of ejecting rollers that eject the recording mediums at the downstream side of the recording portion. Each of the pair of transport rollers and the pair of ejecting rollers has a driving roller and a follower roller. The driving roller of each of the pair of transport rollers and the pair of ejecting rollers is rotatably driven by a common or separate motor. A rotational amount of the driving motor is controlled by a control unit, such that the recording mediums can be transported to the recording portion with a desired transport amount.
However, if kinds of the recording mediums are different from one another, the recording mediums are different from one another in the thickness, material, and weight of the recording medium. As a result, the friction coefficient between each of the driven transport roller and the driven ejecting roller (hereinafter, referred to as rollers) and the recording medium vary. Accordingly, slippage may occur between each of the rollers and the recording mediums per a kind of each of the recording mediums. If the slippage occurs between each of the rollers and the recording mediums, even though each of the roller is driven so as to rotate by a predetermined amount, the recording mediums are not transported as much as a target transport amount due to the slippage. Thereby, recording quality may be lowered. In particular, in an inkjet printer in which in recent years, image quality is exceedingly improved and photo image quality is achieved, paper transport accuracy of order of several micrometers is required. If the paper transport accuracy of order of several micrometers is not satisfied, streaks, that is, a so-called ‘banding phenomenon’ may occur in the recorded photograph. Therefore, the paper feeding accuracy is lowered, thereby notably affecting the recording result.
In this case, the ‘banding phenomenon’ refers to a phenomenon that, if printing and paper (recording medium) transport are continuously performed by a recording head and nozzles for printing of one row in order to perform printing of one row, clogging or an empty space occurs between subsequent printing rows due to the variation in the paper transport accuracy or the variation at locations of the recording head and the nozzles. Accordingly, the printing quality is lowered in not only monochrome printing but also color printing.
Accordingly, in order to resolve the above-mentioned problems, a raster-type recording apparatus is disclosed in JP-A-5-305747 or JP-A-8-72341. The raster-type recording apparatus measures an actual printing length R′ (printing result) with respect to a predetermined printing length R (target value). In addition, since a value of a correction coefficient is calculated from the lengths R and R′, it is possible to correct the transport amount in the actual printing operation by using the correction coefficient.
Further, generally, structures of the transport roller and the ejecting roller, such as materials, are different from each other. Therefore, the transport error when the recording medium is transported by the transport roller, and the transport error when the recording medium is transported by the ejecting roller are different from each other. The structure obtained by considering these points corresponds to a structure of a recording apparatus that is disclosed in JP-A-2004-123313. In JP-A-2004-123313, in the recording apparatus disclosed having a structure in which a plurality of pairs of rollers are provided and the combination of the roller pairs transporting the recording mediums varies, the transport amount of the recording medium can be appropriately corrected.
However, it is not possible to prevent the ‘banding’ phenomenon from occurring by only the above-mentioned correction. For example, until the recording medium is released from a nipping state between the transport roller pair after the trailing end of the recording medium passes through the feed portion, that is, the trailing end is completely passed through, with respect to the variation of the banding phenomenon occurring due to the friction between the trailing end of the recording medium and the transport path, or the variation of the rolling area (contact area) of the recording medium with respect to the transport roller due to the phenomenon that the trailing end of the recording medium automatically descends and the recording medium deforms, that is, the variation of a rolling angle, the consideration is not sufficiently made. For this reason, according to a kind of the paper (thick paper having high rigidity), until the trailing end is completely passed through, the transport amount of the recording medium may vary. As a result, the banding phenomenon may occur.
In this case, the ‘passing through the feed portion’ means that the recording medium passes through the region nipped between the feed roller of the feed portion and the transport path.